A ruthless Triad-style gang implicated in at least 15 violent crimes, including kidnaps and brutal assaults, is being linked to the murder of a young Chinese couple in Newcastle last month.

Detectives investigating the deaths of Zhen Xing Yang and his girlfriend Xi Zhou, both 25, have identified a criminal syndicate from Fujian province of China, a traditional Triad stronghold, which is preying upon young Chinese students across Britain.

Senior officers believe the syndicate, which has struck in London, Manchester and the north-east, is targeting Chinese students through online letting agencies. A lodger who had just moved into the flat rented by Newcastle University graduates Yang and Zhou remains on the run, and police believe that he may have been a 'sleeper' placed by the gang to scout the premises for cash.

Days before Zhou was murdered, she telephoned her mother in China to say that the new lodger 'frightened and unsettled' her. The gang, described by detectives as 'serious operators', have extensive links with Fujian, the birthplace of one of Britain's biggest people-smuggling rackets, which is believed to have brought about 1,000 illegal immigrants into the country over two years. Murder squad officers are confident the motive for the double murder was money. 'Not a single penny' was found in the flat after the killings and a number of valuable items were missing.

Detective Superintendent Steve Wade of Northumbria Police, who is leading the investigation, said: 'We have identified a fairly complex criminal network who are ostensibly targeting Chinese rich kids who are seen as easy pickings and soft targets. We have intelligence of at least 15 cases and there have been a number of kidnaps and attacks, but why this escalated into a double murder in this instance remains speculation.'

Police are investigating incidents in Manchester, a number of kidnappings in London, mainly linked to the Chinatown area of the West End, and a similar case in Newcastle in 2004. Despite a long history of intimidation and violence involving the Chinese community, many cases remain unsolved. The mutilated bodies of two Fujianese were found in bags in east London in 1995 in what detectives described as a typical gangland hit.

Officers believe that such is the fear of organised gangs among the UK's Chinese community that potential witnesses have been too frightened to contact police. Wade admitted he was 'disappointed' with the response. Meanwhile, police are closer to piecing together the details of the latest attack.

New evidence from a gastroenterologist reveals that Zhou was killed within hours of her last meal at 3:30pm at a Wagamama noodle bar in the centre of Newcastle where she worked. They believe Yang was tortured for at least an hour and that his girlfriend was killed shortly after arriving at their flat on the afternoon of Thursday, 7 August. Their bodies were found two days later. Zhou's murder may indicate that she knew the killer, possibly the mystery lodger.

Police, although sceptical, have yet to rule out that Yang was murdered after a dispute with a betting syndicate which may have employed him as an agent to gain an edge in betting on the results of Premier League football games. These are shown in China with up to a minute's delay, offering gambling syndicates with live information a critical advantage. Yang was known to have hired 'spectators' to watch matches.

Wade said: 'We have had calls from fans sitting alongside Chinese people who are relaying football commentary live for the full 90 minutes. It's not just Premier League matches.'

Last week the parents of Yang and Zhou flew to England to appeal for help in finding their killers. Zhou's father said she had been a 'wonderful child', who was 'full of love'. Sanbao Zhou added that the family had 'almost lost the will to live' since the murder.